Putin and Trump are to have their first meeting at the sidelines of the G-20 summit

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In this file photo, Russian President Vladimir Putin attends a meeting to discuss the Ukrainian peace process at the German federal Chancellery on October 19, 2016 in Berlin, Germany. Putin is set to meet President Donald Trump at the G-20 summit later this week.

The Kremlin says its patience with a U.S. plan to return the Russian Embassy's compounds is running out.

President Vladimir Putin's foreign affairs adviser, Yuri Ushakov, said Monday that Russia has demonstrated a remarkable restraint by refraining from a tit-for-tat response to President Barack Obama's decision in December to expel 35 Russian diplomats and shutter Russian compounds in Maryland and on Long Island, New York.

Ushakov says while Russia has shown "unusual flexibility," Moscow's patience "has its limits." He urged Washington to take action to "free Russia from the need to take retaliatory moves," emphasizing that Moscow will feel obliged to respond if the matter isn't settled.

Putin and Trump are to have their first meeting at the sidelines of the G-20 summit, being held in Germany on Friday and Saturday.